The present invention relates generally to the production of glare-reducing windows and the like and, more particularly, to an improved apparatus for shaping the plastic interlayer utilized in bent, laminated safety glass windshields.
Glare-reducing laminated windshields employed in present-day automobiles generally utilize a plastic interlayer having a colored or neutral shaded band extending across the upper marginal edge portion thereof. This band is preferably graduated with the greatest concentration of light-absorbing dye being present nearest the periphery of the plastic interlayer and the concentration thereof diminishing gradually downwardly toward the other edge of the band until finally becoming almost imperceptible at the fade-off line. It has been found that this band greatly reduces the discomfort to the driver and other occupants of the automobile which normally results from direct sun glare through a windshield.
Since the windshield in present autmobile designs is mounted in a tilted or non-vertical attitude and because of the longitudinal curvature of the windshield, the otherwise flat plastic interlayer having a rectilinear colored band must be shaped or warped prior to lamination to obtain a fade-off line which is horizontal and substantially parallel to the horizon when the finished curved windshield is installed in its functional inclined position in the automobile.
In a typical plastic interlayer shaping operation, a plurality of continuous lengths of suitable thermoplastic material are withdrawn from separate supply rolls and, while superimposed one upon the other, are clamped at their free ends in a frame and uniformly stretched or placed in tension. While maintained in this stretched condition, the continuous lengths of plastic also are clamped in the frame along a line remote from the free ends thereof and then cut transversely from the continuous lengths outwardly of the frame to provide a plurality of individual sheets. Thus, the sheets are clamped in the frame along the two opposite transverse edges only. A succession of these frames, each with a plurality of uniformly taut or tensioned sheets clamped therein, are supported in a vertical orientation and moved in spaced relation first through a heating zone and then through a cooling zone. During heating, the sheets become pliable and the central portions, as well as the unsupported edges thereof, sag downwardly by gravity in the plane of the sheets to the desired curvatures or shapes. Sometimes, external tractive forces are applied to the lower, unsupported edges of the sheets to assist in distorting or warping the sheets to the desired curvatures. While maintained in such distorted or warped condition, the sheets are cooled to set the same in these desired shapes.
In order to prevent sticking between the adjacent convolutions of the supply roll of thermoplastic material and to facilitate subsequent dispensing and handling, it is customary to provide a suitable parting agent in the form of a powder between adjacent convolutions. However, the parting agent not only creates a dusty and polluted atmosphere but, more importantly, requires removal, as by washing for example, from the plastic sheets prior to final assembly with the glass panels. As a result, refrigerated thermoplastic material has been developed to obviate the need for a parting material and the disadvantages associated therewith. However, the rigidity of such refrigerated plastic material poses problems in properly stretching and tensioning the same as required by the shaping operation in order to produce glare-reducing windows.